On Tue, Jun 17, 2014 at 06:37:58PM -0400, Waiman Long wrote: > In the __split_huge_page_map() function, the check for > page_mapcount(page) is invariant within the for loop. Because of the > fact that the macro is implemented using atomic_read(), the redundant > check cannot be optimized away by the compiler leading to unnecessary > read to the page structure. > > This patch moves the invariant bug check out of the loop so that it > will be done only once. On a 3.16-rc1 based kernel, the execution > time of a microbenchmark that broke up 1000 transparent huge pages > using munmap() had an execution time of 38,245us and 38,548us with > and without the patch respectively. The performance gain is about 1%. For this low difference it would be nice to average over few runs + stddev. It can easily can be a noise. > Signed-off-by: Waiman Long <Waiman.Long@xxxxxx> But okay: Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>